Pump arrangement with auxiliary cathode for electrical discharge vessels



Feb. 10, 1970 G. HORN ETAL 3,

PUMP ARRANGEMENT WITH AUXILIARY CATHODE FOR ELECTRICAL DISCHARGE VESSEL-S Filed June 27, 1966 INVENTORS GERHAR'D HORN HELMUT KATZ saw ATTORNEYS United States Patent 3,495,116 PUMP ARRANGEMENT WITH AUXILIARY CATH- ODE FOR ELECTRICAL DISCHARGE VESSELS Gerhard Horn and Helmut Katz, Munich, Germany, as-

signors to Siemens Aktieugesellschaft, a corporation of Germany Filed June 27, 1966, Ser. No. 560,471 Claims priority, application Germany, June 30, 1965,

Int. Cl. H01 7/16 US. Cl. 3137 8 Claims ABSTRACT OF THE DISCLOSURE A pump arrangement for installation in an electronic discharge vessel. The pump includes an auxiliary electron discharge path comprising a dispenser cathode of the metal capillary type for producing electrons Which are directed to impinge upon the surface of an impact electrode means. The impact electrode may be of zirconium or titanium and is heated by the electron impact on the surface thereof.

The invention relates to a pump arrangement, utilizing an auxiliary cathode, for electrical discharge vessels, in particular power tubes.

In tubes of higher power, particularly velocity modulated tubes such as in traveling wave tubes, it is becoming more and more important to create a pump arrangement within the tube involved which can bind gas quantities freed during the course of the tube life, and thereby continuously provide for a good vacuum.

At the present, a number of such arrangements are known, which are usually designated by the collective term ion getter pumps. These known pumps, in part, requires a considerable power expenditure, and in addition thereto occupy considerable space because their efficient functioning depends largely upon the size of the surface of the electrode involved, and further, still many require an additional magnetic field. In addition to this, these pumps do not efiiciently bind some gases so that very often these gases which are especially disturbing and frequently occurring in the tubes, for example Ar, He and oxygen, cannot be sufiiciently eliminated.

It is the object of the invention to create a pump arrangement which, as a result of its concentric structure, is suitable for installation, as an additional device, in an appropriate electrical discharge vessel, in particular in power tubes for highest frequencies, and which avoids the previously mentioned disadvantages to as great an extent as possible.

In a pump arrangement as initially described, this is accomplished according to the invention, by the feature that for anauxiliary discharge of great discharge intensity, the auxiliary cathode consists of an indirectly heated storage cathode, in particular of an MK cathode, and that one or several attached operating electrodes are provided, in particular in the form of anodes, especially constructed to achieve a considerable electron impact, with the surface of said electrodes being entirely or partially coated and/ or primarily consisting of getter material such as zirconium or the like.

The invention is based upon the knowledge that electrodes made of a high melting metal with a zirconium or other suitable coating produce an excellent gettering action when they are brought to a sufficiently high temperature that sufficiently intensive appropriates chemical reaction between the zirconium and the gases to be gettered takes place, whereby such gases are then bound 3,495,116 Patented Feb. 10, 1970 with the zirconium. It is advantageous in this arrangement if some of several operating electrodes reach different temperatures during operation, or if only one operating electrode is present, the cross section of the generally disk-shaped electrode involved is proportioned to have a varying thickness, for example, becoming thinner toward its periphery, in such a Way that during electron impact different temperatures exist at the same electrode for the individual gases to be gettered. For example, for the binding of hydrogen, a temperature of approximately 300 is optimum. With respect to the fact that areas of increased temperature and sufficient surface size in high frequency tubes, such as traveling wave tubes, cannot be disposed within the discharge system involved at all, or only with great difficulties, the pump is constructed as an auxiliary discharge system to be additionally installed. For this purpose it is provided with a concentric structure so that it readily can be additionally installed in a discharge vessel. Its efficient pump effect is based upon the excellent qualities of the storage cathode (auxiliary supply cathode) utilized for this purpose, in particular an MK cathode. Such a cathode assures a reliably long life, and in addition has a sutficient current capacity that even when the heater and accelerating voltage requirements are small, the required electrodes with large surfaces may be brought to a desired glow and that, in addition to this feature, by the relatively large discharge current density, a sufficient ionization of the remaining gases is so assured that their binding as an ion to the appropriate getter is accelerated. In this case the discharge can, especially advantageously, take place in the range of saturation.

Further details of the invention will be explained by means of the examples of construction, illustrated purely schematically in the drawings, wherein parts which do not absolutely contribute to the understanding of the invention have been omitted or have not been designated.

In the drawings:

FIG. 1 illustrates an electron discharge system with the cathode portion illustrated in elevation and the anode in transverse section;

FIG. 2 is a similar figure of one embodiment of the invention utilizing a plurality of anode electrodes;

FIG. 3 is a similar figure of an embodiment utilizing two electron emitting surfaces; and

FIG. 4 illustrates an alternate arrangement wherein the operational electrode is concave.

Referring to FIG. 1, which illustrates a very simple construction of a pump arrangement embodying the invention, the MK cathode 1 of cylindrical shape and provided with an emission end surface is cooperable with a disk-shaped operating electrode 2 of molybdenum, operatively disposed in opposition to the cathode, and provided by known methods with a coating of zirconium which may extend on either or both sides of the disk. If a suitable voltage is maintained between the two electrodes, as a result of the impact of the electron discharge from the cathode upon the molybdenum disk, sufficient heat will be generated to effect a desired glow in such a way that the central portion of the disk possesses the highest temperature, which then gradually diminishes towards the periphery of the disk.

This distribution may be adjusted, for example, by selection of an appropriate accelerating voltage, and also by variation of the cross section of the molybdenum disk, in such a way that for the gettering of certain gases, the desired temperatures are achieved.

In the arrangement of FIG. 2 an auxiliary electrode 3 is additionally provided, which is in the form of an apertured diaphragm. This electrode is formed with a central opening, the diameter of which is smaller than that of the :athode. The customary other operating electrode is disposed behind this auxiliary electrode, both electrodes, however, being connected to different high positive po- ;entials relative to the cathode. In this arrangement the liaphragm-shaped first operating electrode receives a part of the discharge current and thereby is brought to a glow by electron impact. The portion of the current pass- .ng through the diaphragm opening strikes the actual, principal operating electrode and, according to the amount )f such current, brings this electrode to a higher or lower )perating temperature. The potential difference between lllCh two operating electrodes provides the feature that my remaining gases present in the space between these we electrodes are ionized because of the occurring elec- .r0r1 discharge, which in particular is of high density, and n addition thereto, the ions formed during such process '6 accelerated towards the two electrodes, which, for :xample, are covered with zirconium, and thus bound hereto.

In the construction illustrated in FIG. 3, the MK :athode is so constructed that its two end surfaces are :onstructed in the form of respective emission material :arrier disks 11 and 12 so that emission takes place at oth ends. By appropriate selection of the distances of he zirconium covered operating electrodes 21 and 22 as vell as by appropriately applied potentials, the individual )perating electrodes are in this example likewise heated y electron impact to different high temperatures so that tn excellent getter effect is obtained for the individual 'emaining gases requiring different getter conditions. The VIK cathode emitting on both ends may, in an advanageous development of the described pump arrangement, also be utilized in such a way that one of its emission faces s operable for beam production in the actual tube system tnd that only the other emitting end surface is utilized or the described pump operation.

FIG. 4 illustrates an alternate arrangement of the pres- :nt invention wherein the impact electrode 32 is concave o somewhat surround the cathode 31. Additionally, the :athode 31 may be convex.

The invention is not restricted to the illustrated exam- )le of construction. Many more possibilities of construcion can be achieved which have not been individually llustrated. In particular, it is advantageously possible to :onstruct the electrode surface, in particular the cathode urface, with a convex or concave formation and to thereay increase the ionization space and with it the ionization :ffect of the discharge space of the auxiliary discharge ystem. For some cases involving special tube types, it nay be advantageous to leave the surface of the operatng electrode arranged opopsite to the emission plane If the cathode free of zirconium. It will also be apparent hat other getter substances, as for example titanium, may ikewise be successfully utilized instead of the mentioned irconium which has a known excellent getter effect.

Changes may be made within the scope and spirit of be appended claims which define what is believed to be ew and desired to have protected by Letters Patent.

We claim:

1. A pump arrangement for operation within an elec- 'ical discharge vessel for preventing gas accumulation 'ithin the vessel, said pump comprising: a cathode, said athode being a metal capillary cathode for emitting a igh density electron stream; impact electrode means ositioned adjacent said cathode and having an impact irface for receiving the electrons emitted by said cathde; and a getter material secured to said impact elec- 'ode means, said impact surface free of getter material, hereby, electron impingement on said impact surface ill cause said impact electrode means to become heated ifficiently to enable said getter material to absorb gases hich may exist within the vessel.

2. A pump arrangement for operation within an elecical discharge vessel for preventing gas accumulation ithin the vessel, said pump comprising: a cathode, said cathode being a metal capillary cathode for emitting a high density electron stream; impact electrode means positioned adjacent said cathode and having an impact surface for receiving the electrons emitted by said cathode and including first and second electrodes, said second electrode being apertured and positioned between said cathode and said first electrode; and a getter material secured to said impact electrode means, whereby, electron impingement on said impact surface will cause said impact electrode means to become heated sufficiently to enable said getter material to absorb gases which may exist Within the vessel.

3. A pump arrangement for operation within an electrical discharge vessel for preventing gas accurnmulation within the vessel, said pump comprising: a cathode, said cathode being a metal capillary cathode for emitting a high density electron stream; impact electrode means including a plurality of individual electrodes, said impact electrode means being positioned adjacent said cathode and having an impact surface for receiving the electrons emitted by said cathode; and a getter materialsecured to said impact electrode means, the individual electrodes arranged with respect to said cathode whereby, electron impingement on said impact surface will cause said impact electrode means to become sufficiently heated with the individual electrodes thereof being heated to different temperatures to enable said getter material to absorb gases which may exist within the vessel.

4. A pump arrangement for operation within an electrical discharge vessel for preventing gas accurnmulation within the vessel, said pump comprising: a cathode, said cathode being a metal capillary cathode for emitting a high density electron stream; impact electrode means positioned adjacent said cathode and having a non-uniform cross-section and an impact surface for receiving the electrons emitted by said cathode; and a getter material secured to said impact electrode means, whereby, electron impingement on said impact surface will produce a temperature gradient across said impact electrode means sufficient to enable said getter material to absorb gases Which may exist within the vessel.

5. A pump arrangement for operation within an electrical discharge vessel for preventing gas accumulation within the vessel, said pump comprising: a cathode, said cathode being a metal capillary cathode for emitting a high density electron stream; and impact electrode means positioned adjacent said cathode and having an impact surface for receiving the electrons emitted by said cathode, said impact electrode means consisting substantially of getter material, whereby electron impingement on said impact surface will cause said impact electrode means to become sufiiciently heated to enable said getter material to absorb gases which may exist within the vessel.

6. A pump arrangement for operation within an electrical discharge vessel for preventing gas accumulation within the vessel, said pump comprising: a cathode, said cathode being a metal capillary cathode for emitting a high density electron stream; impact electrode means positioned adjacent said cathode and having an impact surface for receiving the electrons emitted by said cathode, said impact electrode means including a first electrode formed by a circular sheet of molybdenum and a second electrode formed by an apertured circular sheet of molybdenum and positioned between said cathode and said first electrode; and a getter material secured to said impact electrode means, whereby, electron impingement on said impact surface will cause said impact electrode means to become heated sufficiently to enable said getter material to absorb gases which may exsit Within the vessel.

7. A pump arrangement according to claim 6 wherein said impact electrode means includes a concave surface.

8. A pump arrangement according to claim 7 wherein the getter material is disposed in the center of said concave surface.

(References on following page) 5 6 References Cited 3,299,311 1/1967 Veith et a1. 313-7 UNITED STATES PATENTS 3,319,107 5/1967 W1111ams 313180 B 4/1956 Katz 1 -17 RAYMOND F. HOSSFELD, Primary Examiner 4/1951 Dorgelo 313174 X 2/1961 Johnson et a1 313 1s0 X 5 us. 01. X.R. 8/1966 Grifiiths 313180 X 313-178, 179, 180 

